This application claims the priority benefit of Taiwan application Ser. No. 090122164, filed Sep. 6, 2001.
1. Field of the Invention
This invention relates in general to an apparatus for generating a digital wave and the method thereof. More specifically, this invention relates to an apparatus for generating a digital wave and the method thereof, in which a low frequency clock is used for generating a highly accurate digital wave.
2. Description of Related Art
As the demand for high-capacity storage increases, so does the use of the optical information recording apparatus, such as a rewritable or recordable optical drive. When a writable optical drive writes data to a compact disc rewritable (CD-RW), a laser diode emits the energy required for the data recording. During the entire writing process, the laser diode has to be capable of providing three optical signals of different powers. When the optical signal of a different power illuminates the optical disc, the data area on the optical disc will create a corresponding status due to the different power.
FIG. 1 is a diagram showing the variation of the power of the optical signal for recording corresponding to a data area of the optical disc. The data area of a rewritable optical disc has a space area and a mark area. The data stored in the mark area is constituted by logic xe2x80x9c1xe2x80x9d and logic xe2x80x9c0xe2x80x9d. When the laser beam passes the space area, an optical signal having an erase power PERASE generated by the laser diode must be used to illuminate the optical disc. When the laser beam passes the mark area, an optical signal, alternatively having a write power PWRITE and a bias power PBIAS generated by the laser diode must be used to illuminate the optical disc.
When writing to the mark area, the required times of the optical signal having the write power PWRITE and the bias power PBIAS are determined by the characteristic of the optical disc and the specification of the data to be written. One writing period comprises at least one writing power PWRITE and at least one bias power PBIAS. Therefore, in one writing period T, the writing power PWRITE and the bias power PBIAS are generated according to a highly accurate digital wave W. In general, the digital wave W has to be toggled once or twice within one writing period.
FIG. 2 is an example of a highly accurate digital wave. If a writing period T is divided into n time points, the digital wave W needs to be toggled once or twice within the writing period T. The time point for the toggle state is selected from the n time points. Referring to FIG. 2, the time points for the toggle state are time point 4 and time point 12, FIG. 3 is a block diagram of a conventional apparatus for generating a digital wave. Referring to FIG. 3, the digital wave generating apparatus 300 comprises a counter 310, comparators C1, C2, a multiplexer 312 and flip-flop 314. The counter 310 is used for receiving a high frequency clock signal CLKn. When the high frequency clock signal CLKn finishes one periodic cycle, the counting value C to be outputted from the counter 310 is added by 1. The period of the high frequency clock signal CLKn is one-nth of the writing period T. The comparator C1 is coupled to the counter 310 for receiving the counting value C and the select signal S1 and outputting a comparison signal P1. The comparator C2 is coupled to the counter 310 for receiving the counting value C and the select signal S2 and outputting a comparison signal P2.
The select signal S1 is used for determining the time point at which the digital wave W is toggled from the low level to the high level. The select signal S2 is used for determining the time point that the digital wave W is toggled from the high level to the low level. The multiplexer 312 is coupled to the comparators C1 and C2 for receiving the comparison signals P1 and P2, and then outputting the multiplexing signal m. When the digital wave W is at the low level, the multiplexer 312 outputs the comparison signal P1. When the digital wave W is at the high level, the multiplexer 312 outputs the comparison signal P2. The flip-flop 314 is coupled to the multiplexer 312 for receiving the multiplexing signal m and outputting the digital wave W. When the multiplexing signal m is toggled from the low level to the high level, the digital wave W to be outputted from the flip-flop 314 is also toggled.
Accordingly, the conventional apparatus for generating the highly accurate digital wave requires a high frequency clock signal, having the disadvantages of high cost and being difficult to control the accuracy.
According to the foregoing description, an object of this invention is to provide an apparatus for generating a highly accurate digital wave by using a low frequency clock signal and the method thereof.
Therefore, the invention is to provide an apparatus for generating a digital wave. A period of a basic clock signal is divided into a plurality of time points, and the level of the highly accurate digital wave is toggled at these time points. The apparatus comprises a delay phase lock loop, for generating a plurality of delayed clock signals according to the basic clock signal. The apparatus further comprises a first multiplexer and a second multiplexer, each for outputting one of the delayed clock signals according to the first and the second select signals, respectively. The apparatus further comprises the first and the second edge-triggered flip-flops, for receiving output signals of the first and the second multiplexer respectively. The apparatus further comprises a logic gate for outputting the digital wave according to the outputs of the first and the second edge-toggled flip-flops. The digital wave is toggled according to the first select signal, and then further toggled according to the second select signal.